For a multi-level cell (MLC) NAND flash memory, local self-boosting method is widely used to prevent program disturbance in conventional art. This conventional method locally boosts some of inhibited string region by cutting off channel of memory cell. To inhibit a cell properly, a channel potential of the inhibited cell should be high enough to reduce electrical field across the tunnel oxide to avoid Fowler-Nordheim (FN) tunneling.
As dimension scaling down, a boosting ratio degrades obviously due to large parasitic capacitance. This weak boosting condition is also correlative to data pattern of neighboring cell and the worst case usually happen when neighboring bit line is programmed. In conventional art, some operation methods are proposed to improve this problem, for example, pair bits program scheme. But such schema also worsen program performance. Therefore, providing a program method which can improve boosting potential without performance loss is an important course for an engineer in this art.